How Section 24 changed the maths
Section 24 quietly reshaped landlord economics. Instead of deducting mortgage interest as a cost, individual landlords now add it back to their taxable profit and receive only a basic-rate tax credit: 20% up to 2026/27, rising to 22% from 2027/28. For a higher-rate taxpayer that means paying tax on income you never truly earned, and from 6 April 2027 the rate on that rental slice rises to 42%.
The tax you actually pay
The Rental Income & Section 24 Tax Calculator takes your rent, allowable expenses and mortgage interest and shows the tax you actually pay, side by side with the old pre-2017 rules and a Company comparison. You can toggle between the 2026/27 and 2027/28 tax years to see exactly how the 2027 rise hits you.
SA105 boxes and Making Tax Digital
It also lays out the SA105 self-assessment boxes and flags when Making Tax Digital for Income Tax will apply to you (it applies over £50,000 of qualifying income from April 2026, over £30,000 from April 2027 and over £20,000 from April 2028, counting property and self-employment income together), so the numbers you read are the numbers you file.